avoid crash if caller hangs up during heads-up notification

app/build.gradle

@@ -8,7 +8,7 @@ android {
         applicationId = 'com.tutpro.baresip'
         minSdkVersion 21
         targetSdkVersion 26
-        versionCode = 5
+        versionCode = 7
         versionName = '1.0'
         ndk {
             abiFilters 'armeabi-v7a'

app/src/main/kotlin/com/tutpro/baresip/MainActivity.kt

@@ -521,13 +521,15 @@ class MainActivity : AppCompatActivity() {
                                 if (callButton.tag == "Call") {
                                     callee.setOnKeyListener(null)
                                 }
-                                val caller_heading = layout.findViewById(view_id) as TextView
+                                val caller_heading = layout.findViewById(view_id) as TextView?
+                                if (caller_heading != null) {
                                     val view_index = layout.indexOfChild(caller_heading)
                                     layout.removeViews(view_index, 3 * remove_count)
                                     val callsIn = Call.uaCalls(calls, ua, "in")
                                     for (i in inIndex until callsIn.size) {
                                         addCallViews(ua, callsIn[i], (i + 1) * 10)
                                     }
+                                }
                                 historyButton.visibility = View.VISIBLE
                             }
                             if (!call.hasHistory) {
@@ -613,12 +615,6 @@ class MainActivity : AppCompatActivity() {
         }
     }
 
-     override fun onAttachedToWindow() {
-        super.onAttachedToWindow()
-         Log.d("Baresip", "View count at onAttachedToWindow is ${layout.childCount}")
-         Toast.makeText(this, "Hi UI is fully loaded", Toast.LENGTH_SHORT).show();
-    }
-
     override fun onBackPressed() {
         moveTaskToBack(true)
     }